1. Field
The present disclosure generally relates to a system and method for generating a carbon dioxide stream. More particularly, the present disclosure relates to generating a carbon dioxide stream in a flue gas stream processing system employing a chemical looping combustion system.
2. Related Art
Chemical looping combustion (CLC) is a combustion technology that affords inherent separation of carbon dioxide (CO2). Typically, CLC employs two reactors: an air reactor and a fuel reactor. A solid oxygen carrier, which may be a metal, transfers the oxygen from the air to the fuel. The fuel is fed to the fuel reactor where it is oxidized by the oxygen carrier and the oxygen is carrier is reduced and retuned to the air reactor, where it is oxidized and the loop of oxidizing the fuel and reducing the carrier continues. The exit stream from the fuel reactor, commonly referred to as the flue gas, typically contains CO2 and water vapor. However, depending on the fuel, the flue gas may also contain trace contaminants. The water vapor in the flue gas is separated from the CO2 by cooling and condensation, while the CO2 is liquefied or compressed for further transport.
Due to its limited residence time in the fuel reactor and the lack of free oxygen, the CO2 stream may be contaminated with products of incomplete combustion, such as carbon monoxide (CO), hydrogen (H2), and methane (CH4). Additionally, the flue gas stream may be diluted with air, which may in-leak to the boiler.
Contaminants such as CO, H2, and CH4 are more difficult to liquefy than CO2 during liquification of the CO2. The contaminants take the form of a non-condensable phase commonly referred to as a exhaust gas. The level of contaminates within the exhaust gas as is often too high to be released to the atmosphere without further treatment. Recycling of the exhaust gas to the fuel reactor would result in gradual accumulation of N2 and other inert gases in the flue gas and may also dilute the CO2 stream, thereby reducing the efficiency of the CLC system.
Accordingly, a method or system for processing the exhaust gas in an efficient way without impacting the CLC system is desired.